Fiber optic ribbon cable having enhanced ribbon stack coupling and methods thereof

ABSTRACT

A fiber optic ribbon cable includes a jacket of the cable, the jacket having a cavity defined therein, an optical element including an optical fiber and extending within the cavity of the jacket, and a dry water-blocking element extending along the optical element within the cavity. The dry water-blocking element is wrapped around the optical element with at least a portion of the dry water-blocking element disposed between another portion of the dry water-blocking element and the optical element, thereby defining an overlapping portion of the dry water-blocking element. The optical element interfaces with the overlapping portion to provide direct or indirect coupling between the optical element and the jacket.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/222,417, filed on Dec. 17, 2018, which is a continuation of U.S.patent application Ser. No. 15/972,692, filed on May 7, 2018, now U.S.Pat. No. 10,180,552, which is a continuation of U.S. patent applicationSer. No. 15/410,104, filed on Jan. 19, 2017, now U.S. Pat. No.9,964,724, which is a continuation of U.S. patent application Ser. No.14/863,721, filed on Sep. 24, 2015, now U.S. Pat. No. 9,594,224, whichis a continuation of US. patent application Ser. No. 13/625,052, filedon Sep. 24, 2012, now U.S. Pat. No. 9,170,388, which claims the benefitof priority to U.S. Provisional Application Ser. No. 61/541,142, filedon Sep. 30, 2011, the content of each of which is relied upon andincorporated herein by reference in its entirety. The benefit ofpriority under 35 U.S.C. § 120 is hereby claimed.

BACKGROUND Field of the disclosure

The present disclosure relates generally to fiber optic cables. Morespecifically, the disclosure relates to a dry fiber optic ribbon cablethat includes an overlapping tape for protecting at least one fiberoptic ribbon stack and providing a ribbon coupling force.

Technical field

Fiber optic cables include optical waveguides such as optical fibersthat transmit optical signals, for example, voice, video, and/or datainformation. One type of fiber optic cable configuration includes anoptical waveguide disposed within a tube, thereby forming a tubeassembly. Generally speaking, the tube protects the optical waveguide;however, the optical waveguide must be further protected within thetube. For instance, the optical waveguide should have some relativemovement between the optical waveguide and the tube to accommodatebending. On the other hand, the optical waveguide should be adequatelycoupled with the tube, thereby inhibiting the optical waveguide frombeing displaced within the tube when, for example, pulling forces areapplied to install the cable. Additionally, the tube assembly shouldinhibit the migration of water therein. Moreover, the tube assemblyshould be able to operate over a range of temperatures without undueoptical performance degradation.

Some optical tube assemblies meet these requirements by filling the tubewith a thixotropic material such as grease 1 (FIG. 1). Thixotropicmaterials generally allow for adequate movement between the opticalwaveguide and the tube, cushioning, and coupling of the opticalwaveguide. Additionally, thixotropic materials are effective forblocking the migration of water within the tube. However, thethixotropic material must be cleaned from the optical waveguide beforeconnectorization of the same. Cleaning the thixotropic material from theoptical waveguide is a messy and time-consuming process. Moreover, theviscosity of thixotropic materials is generally temperature dependent.Due to changing viscosity, the thixotropic materials can drip from anend of the tube at relatively high temperatures and the thixotropicmaterials may cause optical attenuation at relatively low temperatures.

Cable designs have attempted to eliminate thixotropic materials from thetube, but the designs are generally inadequate because they do not meetall of the requirements and/or are expensive to manufacture. One examplethat eliminates the thixotropic material from the tube is U.S. Pat. No.4,909,592, which discloses a tube having water-swellable tapes 2 (FIG.2) and/or yarns disposed therein, where the water-swellable tapes 2relatively thin and do not fill the space inside a buffer tube.Consequently, the water-swellable tapes may not provide adequatecoupling for the optical waveguides because of the unfilled space.Additionally, the space may allow water within the tube to migrate alongthe tube, rather than be contained by the water-swellable tape. Thus,such a design may require a large number of water-swellable componentswithin the tube for adequately coupling the optical fibers with thetube, which is not economical because it increases the manufacturingcomplexity along with the cost of the cable.

Another example that eliminates the thixotropic material from a fiberoptic cable is U.S. Pat. No. 6,278,826, which discloses a foam having amoisture content greater than zero that is loaded with super-absorbentpolymers. The moisture content of the foam is described as improving theflame-retardant characteristics of the foam. Likewise, the foam of thisdesign is relatively expensive and increases the cost of the cable.

No admission is made that any reference cited herein constitutes priorart. Applicant expressly reserves the right to challenge the accuracyand pertinence of any cited documents.

SUMMARY

One aspect of the disclosure relates to a fiber optic ribbon cable thatincludes a jacket of the cable, the jacket having a cavity definedtherein, an optical element including an optical fiber and extendingwithin the cavity of the jacket, and a dry water-blocking elementextending along the optical element within the cavity. The drywater-blocking element is wrapped around the optical element with atleast a portion of the dry water-blocking element disposed betweenanother portion of the dry water-blocking element and the opticalelement, thereby defining an overlapping portion of the drywater-blocking element. The optical element interfaces with theoverlapping portion to provide direct or indirect coupling between theoptical element and the jacket.

An aspect of the disclosure relates to a fiber optic ribbon cable,having a jacket and a buffer tube disposed in the jacket, the buffertube having an average inner width, an average inner perimeter lengthand an average cross-sectional inner area. A fiber optic ribbon stackmay extend longitudinally within the buffer tube, the ribbon stackhaving an average cross sectional ribbon area, the inner area and theribbon area defining a ratio of about 0.30 or greater. The ribbon cablefurther may include an elongated tape extending along the ribbon stack,the elongated tape wrapping around the ribbon stack with at least aportion of one opposing edge tucking between the other opposing edge andthe ribbon stack, defining an overlapping portion, the overlappingportion being at least 45 degrees.

In another aspect of the disclosure, the fiber optic ribbon cable mayinclude an overlapping portion of from about 90 degrees to about 130degrees, and in yet other embodiments the overlapping portion may beabout 130 degrees. The overlapping portion may extend along the ribbonstack at least one meter.

In another aspect of the disclosure, the ribbon stack may be coupled tothe fiber optic ribbon cable, having a coupling force of at least 0.39Newtons per meter over a 30 meter length of cable. In some embodiments,the coupling force may be up to about 2.25 Newtons per meter over a 30meter length of cable.

Another aspect of the disclosure provides for a method of manufacturinga fiber optic ribbon cable, including paying off a plurality of opticalfiber ribbons; paying off at least one elongated tape; placing theelongated tape around the plurality of optical fiber ribbons so that theelongated tape wraps around the ribbon stack with at least a portion ofone opposing edge tucking between the other opposing edge and the ribbonstack, defining an overlapping portion of at least 45 degrees, theoverlapping portion at least partially surrounding the plurality ofoptical fiber ribbons, forming a core; extruding a buffer tube aroundthe core; and extruding a cable jacket around the buffer tube.

Another aspect of the disclosure provides for a method of inducing acoupling force in a fiber optic ribbon cable, including providing afiber optic ribbon stack, the ribbon stack having an induced helicaltwist; providing an elongated tape along the fiber optic ribbon stack;placing the elongated tape around the fiber optic ribbon stack, forminga core; creating an overlapping portion of the elongated tape, theoverlapping portion at least partially surrounding the fiber opticribbon stack, the section of the cable comprising at least three layersof the elongated tape extending along the ribbon stack due to theoverlapping portion; extruding a buffer tube around the core, the buffertube comprising a polymer extruded in a molten state; cooling the buffertube, the cooling buffer tube contracting during cooling, inducing acoupling force between the ribbon stack, the elongated tape, theoverlapping portion and the buffer tube of about 0.39 N/m or greater;and extruding a jacket around the buffer tube.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments, andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fiber optic cable having aconventional grease filled tube assembly;

FIG. 2 is a cross-sectional view of a fiber optic cable having aconventional dry tube assembly;

FIG. 3 is a cross-sectional view of a tube assembly according to thepresent disclosure;

FIG. 3a is a cross-sectional view of another tube assembly according tothe present disclosure;

FIG. 4 is a cross-sectional view of the dry insert of the tube assemblyof FIG. 3;

FIG. 4a is a cross-sectional view of another dry insert according to thepresent disclosure;

FIGS. 4b-4d depict various configurations of an adhesive/glue applied tothe dry insert of FIG. 4;

FIGS. 5 and 5 a are cross-sectional views of tube assemblies accordingto the present disclosure having the dry insert of FIG. 4 a;

FIG. 6 is a schematic representation of a manufacturing line accordingto the present disclosure;

FIG. 7 is a cross-sectional view of a fiber optic cable according to thepresent disclosure using the tube assembly of FIG. 3;

FIG. 8 is a cross-sectional view of a fiber optic cable according to thepresent disclosure using the tube assembly of FIG. 5;

FIG. 9 is a perspective view of another dry insert according to theconcepts of the present disclosure;

FIG. 10 is a cross-sectional view of another dry insert according to theconcepts of the present disclosure;

FIG. 11 is a perspective view of another dry insert according to theconcepts of the present disclosure;

FIG. 12 is a perspective view of another dry insert according to theconcepts of the present disclosure;

FIG. 13 is a cross-sectional view of a fiber optic cable with an armorlayer according to the present disclosure;

FIG. 14 is a cross-sectional view of a tubeless fiber optic cableaccording to the present disclosure;

FIG. 15 is a cross-sectional view of a fiber optic cable having strandedtubes according to the present disclosure;

FIG. 16 is a cross-sectional view of the dry insert of FIG. 4a having anadditional layer;

FIG. 17 is a cross-sectional view of still another embodiment of the dryinsert according to the present disclosure;

FIG. 18 is a plan view of the dry insert of FIG. 17;

FIGS. 19 and 20 are cross-sectional views of tubeless fiber optic cablesaccording to the present disclosure;

FIG. 21 is a perspective view of a fiber optic ribbon cable having anoverlapping elongated tape;

FIG. 22 is a cross sectional schematic view of the cable of FIG. 21;

FIG. 23 is a cross sectional view of the cable of FIG. 21;

FIG. 24 is another cross sectional view of the cable of FIG. 21;

FIG. 25 is a partial perspective view of an elongated tape; and

FIG. 26 is a graph showing coupling force of the cable of FIG. 21.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings showing preferred embodiments ofthe disclosure. The disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat the disclosure will fully convey the scope of the disclosure tothose skilled in the art. The drawings are not necessarily drawn toscale but are configured to clearly illustrate the disclosure.

Illustrated in FIG. 3 is an exemplary tube assembly 10 according to oneaspect of the present disclosure. Tube assembly 10 includes at least oneoptical waveguide 12, at least one dry insert 14, and a tube 18. In thiscase, the at least one optical waveguide 12 is in the form of a stack ofribbons 13 having a diagonal D dimension across the corners of thestack. Dry insert 14 generally surrounds the at least one opticalwaveguide 12 and forms core 15, which is disposed within tube 18. Dryinsert 14 performs functions such as cushioning, coupling, inhibitingthe migration of water, and accommodates bending. Dry insert 14 isadvantageous because the optical waveguides are easily removed therefromwithout leaving a residue or film that requires cleaning beforeconnectorization. Moreover, unlike conventional thixotropic materials,dry insert 14 does not change viscosity with temperature variations orhave a propensity to drip from an end of the tube at high temperatures.Furthermore, tube assembly 10 can include other suitable components suchas a polyester binder thread 17 to hold dry insert 14 about opticalwaveguide 12. Likewise, two or more threads may be stitched together forholding dry insert 14 together before extruding tube 18 therearound.FIG. 3a shows tube assembly 10′, which is a variation of tube assembly10. Specifically, tube assembly 10′ includes a plurality of looseoptical waveguides 12, instead of the stack of ribbons 13. In this case,tube assembly 10′ includes twenty-four loose optical waveguides 12having diagonal dimension D, but any suitable number of opticalwaveguides may be used. Moreover, optical waveguides 12 may be bundledinto one or more groups using binders, water-swellable threads, tapes,wraps, or other suitable materials. Additionally, tube assemblies 10 or10′ can be a portion of cable as shown in FIG. 7. Furthermore, dryinserts 14 according to the present disclosure may be used with tubelesscable designs.

As depicted, optical waveguide 12 is an optical fiber that forms aportion of an optical fiber ribbon. In this case, the optical waveguidesare a plurality of single-mode optical fibers in a ribbon format thatform ribbon stack 13. Ribbon stack 13 can include helical or S-Zstranding. Additionally, other types or configurations of opticalwaveguides can be used. For example, optical waveguide 12 can bemulti-mode, pure-mode, erbium doped, polarization-maintaining fiber,other suitable types of light waveguides, and/or combinations thereof.Moreover, optical waveguide 12 can be loose or in bundles. Each opticalwaveguide 12 may include a silica-based core that is operative totransmit light and is surrounded by a silica-based cladding having alower index of refraction than the core. Additionally, one or morecoatings can be applied to optical waveguide 12. For example, a softprimary coating surrounds the cladding, and a relatively rigid secondarycoating surrounds the primary coating. In one embodiment, one or moreoptical waveguides 12 include a coating system as disclosed in U.S.patent application Ser. No. 10/632,219 filed on Jul. 18, 2003, thedisclosure of which is incorporated herein by reference. Opticalwaveguide 12 can also include an identifying means such as ink or othersuitable indicia for identification. Suitable optical fibers arecommercially available from Corning Incorporated of Corning, New York.

In other embodiments, ribbon stack 13 can have a corner opticalwaveguide(s) 12 a with a predetermined MAC number, thereby inhibitingoptical attenuation of the corner optical waveguide when subjected tocompressive forces. Stated another way, selecting corner opticalwaveguides with a predetermined MAC number places optical waveguidesthat are less sensitive to optical attenuation from compressive forcesin ribbon stack locations that experience relatively high levels ofcompression. As used herein, MAC number is calculated as a mode fielddiameter (MFD) divided by a cutoff wavelength for the given opticalwaveguide 12 a where both quantities are expressed in micrometers sothat the MAC number is dimensionless. In other words, MFD is typicallyexpressed in micrometers and cutoff wavelength is typically expressed innanometers, so the cutoff wavelength must be divided by 1000 to convertit to micrometers, thereby yielding a dimensionless MAC number.

In one embodiment, one or more of the corner optical waveguides 12 ahave a predetermined MAC number. Specifically, the MAC number is about7.35 or less, more preferably about 7.00 or less, and most preferablyabout 6.85 or less. By way of example, corner optical waveguide(s) 12 ais selected with a MFD of 9.11 μm or less and a cutoff wavelength of1240 nm or more, thereby yielding 7.35 or less for the MAC number.Generally speaking, the MAC number is directly proportional to MFD andinversely proportional to the cutoff wavelength. Ribbon stack 13 hasfour corner optical waveguides 12 a; however, other ribbon stackconfigurations can include more corner positions. For instance, a ribbonstack having a generally plus sign shape includes eight outer corners.Likewise, other ribbon stack configurations may have other numbers ofcorner positions.

Additionally, ribbon embodiments of the present disclosure may have apositive excess ribbon length (ERL), although a negative ERL ispossible. As used herein, ERL is defined as the length of the particularribbon minus the length of the tube or cable containing the ribbondivided by the length of the tube or cable containing the ribbon, whichcan be expressed as a percentage by multiplying by 100. Whether the ERLis calculated using the tube length or the cable length depends on theparticular configuration. Moreover, individual ribbons of a cable canhave different values of ERL. By way of example, ribbons of the cablehave a positive ERL, preferably a positive ERL in the range of about0.0% to about 0.2% or greater. Likewise, embodiments having loose orbundled optical fibers may include a positive excess fiber length (EFL).

FIGS. 4 and 4 a illustrate cross-sectional views of explanatory dryinserts 14 according to the present disclosure. Dry inserts 14 areformed from an elongate material or materials that are capable of beingpaid off from a reel for a continuous application during manufacture.Dry inserts 14 may be formed from a plurality of layers (FIG. 4) thatcan perform different functions; however, dry insert 14 (FIG. 4a ) canalso be a single layer such as a felt material that is compressible. Dryinsert 14 cushions optical waveguide 12 from tube 18, therebymaintaining optical attenuation of optical waveguide 12 below about 0.4dB/km at a reference wavelength of 1310 nm and 0.3 dB/km at a referencewavelengths of 1550 nm and 1625 nm. In one embodiment, dry insert 14 isformed from two distinct layers and/or materials. For instance, FIG. 4depicts a first layer 14 a of dry insert 14 that is a compressible layerand second layer 14 b that is a water-swellable layer. In this case,first layer 14 a is formed from a compressible material having apredetermined spring constant for providing adequate couplingcharacteristics. By way of example, the first layer is a foam tape,preferably, an open cell foam tape; however, any suitable compressiblematerial can be used such as a closed cell foam tape. Second layer 14 bis a water-swellable layer such as a tape having a water-swellablepowder that inhibits the migration of water within tube 18.Additionally, single layer dry inserts according to the presentdisclosure can have similar characteristics.

FIG. 4a depicts another dry insert 14 having a single, non-woven layerof felt made of one or more materials. In this case, dry insert 14comprises a plurality of water-swellable filaments 24 a along with otherfilaments 24 b that are non-swellable in water, thereby forming a layerof felt having multiple materials. As used herein, felt means a materialcomprising one or more types of non-continuous filaments and/or fiberswhich have been caused to adhere and mat together through the action ofheat, moisture, chemicals, pressure, or a combination of the foregoingactions, thereby forming a relatively thick and compressible layer.Water-swellable filaments 24 a may comprise any suitable water-swellablematerial, but preferably include at least one superabsorbant polymer.Preferred superabsorbent polymers are partially cross-linked polymersthat absorb many times their own weight in water and swell considerablywithout dissolving, for example, acrylate, urethane or cellulosic-basedmaterials. By way of example, the single layer dry insert 14 of FIG. 4amay include about 25% or less by weight of water-swellable filaments 24a and about 75% or more by weight of other filaments 24 b; however,other suitable ratios are possible. Likewise, in this configuration thedensity of the dry insert can be influenced to meet the needs of thetube assembly. Generally speaking, the single layer felt dry insert is acompressible layer for cushioning and coupling of the optical fibers andmay include water-swellable materials for inhibiting the migration ofwater. Unlike some water-swellable tapes the single layer felt has arelatively large thickness that generally speaking fills spaces withinthe tube or cavity. Moreover, the felt dry insert may usewater-swellable filaments that aid in providing compressibility orfluffiness of the dry insert, rather than water-swellable powders thatare used in other water-swellable tapes.

Other filaments 24 b may include any suitable filament and/or fibermaterial such as polymer filaments like polypropylene, polyethylene, andpolyesters, likewise, other suitable materials such as cottons, nylon,rayons, elastomers, fiberglass, aramids, polymers, rubber-basedurethanes, composite materials and/or blends thereof may be included asa portion of other filaments 24 b and may be tailored for providingspecific characteristics. For instance, polymer filaments can be usedfor coupling the dry insert with the tube when the same is extrudedthereover. In other words, the hot tube extrudate at least partiallymelts the polymer filaments, thereby causing adhesion between the two.Another example is that elastomeric fibers can be included in the dryinsert for providing improved coupling of optical waveguide 12 with tube18. The use of elastomeric fibers, or other suitable material, may allowfor the coupling of dry insert 14 to tube 18, and/or optical waveguide12 to dry insert 14 by increasing a coefficient of friction. Of course,as depicted in FIGS. 4b-4d adhesives, glues, (FIGS. 4b-4d ) or othermethods may be used for attaching the dry insert to the tube.Furthermore, the dry insert may include other chemicals or additives toinfluence properties such as flame-retardance.

FIGS. 5 and 5 a depict tube assemblies 30 and 30′ that are similar totube assemblies 10 and 10′ depicted in FIGS. 3 and 3 a, except theyemploy the dry insert of FIG. 4a . Furthermore, tube assemblies 30 and30′ can be included as a portion of a fiber optic cable 60 as depictedin FIG. 8. Dry insert 14 of FIG. 4a advantageously performs thefunctions of cushioning, coupling, inhibiting the migration of water,and accommodates bending like the multi-layer dry insert. Additionally,the single layer construction may reduce costs and improve cablemanufacturability.

Additionally, the dry insert of FIG. 4a can include one or more otherlayers in addition to the felt for tailoring performancecharacteristics. Illustratively, FIG. 16 depicts another dry insert 14having a second layer 162 attached to one side of the felt dry insert ofFIG. 4a . Using a second layer attached to the felt dry insert allowsfor several different dry insert configurations. For instance, the feltdry insert may exclude water-swellable filaments, and instead secondlayer 162 is a water-swellable tape that inhibits the migration ofwater. In another embodiment, the felt includes water-swellablefilaments and a water-swellable tape attached thereto. In a furtherembodiment, second layer 162 is a meltable layer having a polymer thatat least partially melts during extrusion of the tube thereover.Likewise, other dry insert embodiments are possible.

Illustratively, FIGS. 17 and 18 depict dry insert 14 having a first anda second layer 172,176 with at least one water-swellable layer 174disposed in a compartment 174 a therebetween. In other words,water-swellable layer 174 is generally contained in one or morecompartments 174 a between first and second layers 172,176 that act asbacking layers. By way of example, first and second layers may be formedof nylon, polymers, fiberglass, aramid, w-s tape, composite materials,or any other suitable materials in a tape-like configuration. Materialsfor this configuration should provide the necessary strength to endurethe cabling process and intended use. Additionally, at least one of thefirst and/or second layers should be porous for water penetration.Preferably, water-swellable layer 174 includes non-continuouswater-swellable filaments loosely disposed between first and secondlayers 172,174, thereby forming a compressible dry insert. Suitablewater-swellable filaments are, for example, LANSEAL materials availablefrom Toyobo of Osaka, Japan or OASIS materials available from TechnicalAbsorbents Ltd. of South Humberside, United Kingdom. Additionally,water-swellable layer 174 may comprise a water swellable powder alongwith the water swellable filaments. Moreover, water-swellable layer 174may include other filaments as a filler to increase the thickness of thewater swellable layer and thus of the dry insert, while reducing thecost of the dry insert. The other filaments may comprise any suitablenon-swellable as discussed herein.

Furthermore, first and second layers 172,176 are attached together sothat water-swellable layer 174 is generally sandwiched therebetween,thereby creating one or more compartments 174 a, which generallyspeaking traps water-swellable layer 174 therein. At a minimum, layers172,176 are attached together at a plurality of seams 178 along thelongitudinal edges, but are attachable in other ways. Layers 172,176 areattachable using adhesives, heat where appropriate, stitching, or othersuitable methods. In preferred embodiments, layers 172,176 are attachedat intermediate positions along the length of the dry insert. As shownin FIG. 18, layers 172,176 are attached together using a diamond patternof seams 178; however, other suitable patterns such as triangular,semi-circular, or curvilinear patterns are possible, thereby creatingthe plurality of compartments 174 a. Additionally, the seams betweencompartments can be arranged for aiding in forming the dry insert aboutthe optical waveguides. Compartmentalization of water-swellable layer174 advantageously inhibits moving or shifting of the material beyondthe individual compartment. Moreover, the compartments add a pillowytexture to the dry insert.

In further embodiments, first and second layers 172,176 need notcomprise the same material. In other words, the materials of the firstand second layers may be selected to tailor the dry insert behavioraccording to the needs of each side of the dry insert. For instance, thefirst layer is tailored to adhere with the extruded tube and the secondlayer is tailored to have a smooth finish for contact with the opticalwaveguides. Additionally, in other embodiments the dry insert can havemore than a first and second layers to, for instance, optimize theattachment of the layers, coupling, and/or inhibit water migration.However, the dry insert should not be so stiff that it is too difficultto manufacture into a cable assembly. Additionally, as shown in FIG. 4ait may be advantageous for one of the longitudinal edges of any of thedry inserts to have a tapered edges 24 c so that the longitudinal edgesmay overlap without a large bulge when the dry insert is formed aboutthe at least on optical fiber 12.

Dry inserts 14 of the present disclosure preferably have a water-swellspeed so that the majority of swell height of the water-swellablesubstance occurs within about 120 seconds or less of being exposed towater, more preferably about 90 seconds or less. Additionally, dryinserts 14 preferably has a maximum swell height of about 18 mm fordistilled water and about 8 mm for a 5% ionic water solution, i.e., saltwater; however, dry inserts with other suitable maximum swell heightsmay be used.

Dry inserts 14 may be compressed during assembly so that it provides apredetermined normal force that inhibits optical waveguide 12 from beingeasily displaced longitudinally along tube 18. Dry inserts 14 preferablyhave an uncompressed height h of about 5 mm or less for minimizing thetube diameter and/or cable diameter; however, any suitable height h canbe used for dry inserts 14. By way of example, a single layer dry insert14 can have an uncompressed height in the range of about 0.5 mm to about2 mm, thereby resulting in a tube assembly having a relatively smalldiameter. Moreover, height h of dry insert 14 need not be constantacross the width, but can vary, thereby conforming to thecross-sectional shape of the optical waveguides and providing improvedcushioning to improve optical performance (FIG. 12). Compression of dryinsert 14 is actually a localized maximum compression of dry insert 14.In the case of FIG. 3, the localized maximum compression of dry insert14 occurs at the corners of the ribbon stack across the diameter.Calculating the percentage of compression of dry insert 14 in FIG. 3requires knowing an inner diameter of tube 18, a diagonal D dimension ofthe ribbon stack, and an uncompressed height h of dry insert 14. By wayof example, inner diameter of tube 18 is 7.1 mm, diagonal D of theribbon stack is 5.1 mm, and the uncompressed height h of dry insert 14across a diameter is 3.0 mm (2 times 1.5 mm). Adding diagonal D (5.1 mm)and the uncompressed height h of dry insert 14 across the diameter (3.0mm) yields an uncompressed dimension of 8.1 mm. When placing the ribbonstack and dry insert 14 and into tube 18 with an inner diameter of 7.1mm, dry insert is compressed a total of 1 mm (8.1 mm-7.1 mm). Thus, dryinsert 14 is compressed by about thirty percent across the diameter oftube 18. According to the concepts of the present disclosure thecompression of dry insert 14 is preferably in the range of about 10% toabout 90%; however, other suitable ranges of compression may provide thedesired performance. Nonetheless, the compression of dry insert 14should not be so great as to cause undue optical attenuation in any ofthe optical waveguides.

In other embodiments, first layer 14 a of dry insert 14 is uncompressedin tube assembly 10, but begins to compress if optical waveguidemovement is initiated. Other variations include attaching, bonding, orotherwise coupling a portion of dry insert 14 to tube 18. For example,adhesives, glues, elastomers, and/or polymers 14 c are disposed on aportion of the surface of dry insert 14 that contacts tube 18 forattaching dry insert 14 to tube 18. Additionally, it is possible tohelically wrap dry insert 14 about optical waveguide 12, instead ofbeing longitudinally disposed. In still further embodiments, two or moredry inserts can be formed about one or more optical waveguides 12 suchas two halves placed within tube 18.

Other embodiments may include a fugitive glue/adhesive for couplingcable core 15 and/or dry insert 14 with tube 18. The glue/adhesive orthe like is applied to the radially outward surface of dry insert 14,for instance, during the manufacturing process. The fugitiveglue/adhesive is applied while hot or melted to the outer surface of dryinsert 14 and then is cooled or frozen when the cable is quenched orcools off. By way of example, a suitable fugitive glue is available fromNational Starch and Chemical Company of Bridgewater, N.J. under thetradename LITE-LOK® 70-003A. The fugitive glue or other suitableadhesive/material may be applied in beads having a continuous or anintermittent configuration as shown in FIGS. 4b-4d . For instance, oneor more adhesive/glue beads may be longitudinally applied along the dryinsert, longitudinally spaced apart beads, in a zig-zag bead along thelongitudinal axis of the dry insert, or in any other suitableconfiguration.

In one application, a plurality of beads of fugitive glue/adhesive orthe like is applied to dry insert 14. For instance, three continuous, ornon-continuous, beads can be disposed at locations so that when the dryinsert is formed about the ribbon stack the beads are about 120 degreesapart. Likewise, four beads can be disposed at locations so they areabout 90 degrees apart when the dry insert is formed about the opticalwaveguides. In embodiments having the beads spaced apart along thelongitudinal axis, the beads may have a longitudinal spacing S of about20 mm and about 800 mm or more; however, other suitable spacing may beused. Additionally, beads may be intermittently applied for minimizingthe amount of material required, thereby reducing manufacturing expensewhile still providing sufficient coupling/adhesion.

Since tube assemblies 10 are not filled with a thixotropic material thetube may deform or collapse, thereby forming an oval shaped tube insteadof a round tube. U.S. patent application Ser. No. 10/448,509 filed onMay 30, 2003, the disclosure of which is incorporated herein byreference, discusses dry tube assemblies where the tube is formed from abimodal polymeric material having a predetermined average ovality. Asused herein, ovality is the difference between a major diameter D1 and aminor diameter D2 of tube 18 divided by major diameter D1 and multipliedby a factor of one-hundred, thereby expressing ovality as a percentage.Bimodal polymeric materials include materials having at least a firstpolymer material having a relatively high molecular weight and a secondpolymer material having a relatively low molecular weight that aremanufactured in a dual reactor process. This dual reactor processprovides the desired material properties and should not be confused withsimple post reactor polymer blends that compromise the properties ofboth resins in the blend. In one embodiment, the tube has an averageovality of about 10 percent or less. By way of example, tube 18 isformed from a HDPE available from the Dow Chemical Company of Midland,Mich., under the tradename DGDA-2490 NT.

Coupling of the optical waveguide in the tube assembly may be measuredusing a normalized optical ribbon pullout force test. The ribbon pulloutforce test measures the force (N/m) required to initiate movement of aribbon stack from a 10-meter length of cable. Of course, this test isequally applicable to loose or bundled optical waveguides. Specifically,the test measures the force required to initiate movement of a stack ofribbons, or other configurations of optical waveguides, relative to thetube and the force is divided by the length of the cable, therebynormalizing the optical ribbon pullout force. Preferably, the ribbonpullout force is in the range of about 0.5 N/m and about 5.0 N/m, morepreferably, in the range of about 1 N/m to about 4 N/m.

FIG. 6 schematically illustrates an exemplary manufacturing line 40 fortube assembly 10 according to the present disclosure. Manufacturing line40 includes at least one optical waveguide payoff reel 41, a dry insertpayoff reel 42, an optional compression station 43, an glue/adhesivestation 43 a, a binding station 44, a cross-head extruder 45, a watertrough 46, and a take-up reel 49. Additionally, tube assembly 10 mayhave a sheath 20 therearound, thereby forming a cable 50 as illustratedin FIG. 7. Sheath 20 can include strength members 19 a and a jacket 19b, which can be manufactured on the same line as tube assembly 10 or ona second manufacturing line. The exemplary manufacturing processincludes paying-off at least one optical waveguide 12 and dry insert 14from respective reels 41 and 42. Only one payoff reel for opticalwaveguide 12 and dry insert 14 are shown for clarity; however, themanufacturing line can include any suitable number of payoff reels tomanufacture tube assemblies and cables according to the presentdisclosure. Next, dry insert 14 is compressed to a predetermined heighth at compression station 43 and optionally an adhesive/glue is appliedto the outer surface of dry insert 14 at station 43 a. Then dry insert14 is generally positioned around optical waveguide 12 and if desired abinding station wraps or sews one or more binding threads around dryinsert 14, thereby forming core 15. Thereafter, core 15 is feed intocross-head extruder 45 where tube 18 is extruded about core 15, therebyforming tube assembly 10. Tube 18 is then quenched in water trough 46and then tube assembly 10 is wound onto take-up reel 49. As depicted inthe dashed box, if one manufacturing line is set-up to make cable 50,then strength members 19 a are paid-off reel 47 and positioned adjacentto tube 18, and jacket 19 b is extruded about strength members 19 a andtube 18 using cross-head extruder 48. Thereafter, cable 50 passes into asecond water trough 46 before being wound-up on take-up reel 49.Additionally, other cables and/or manufacturing lines according to theconcepts of the present disclosure are possible. For instance, cablesand/or manufacturing lines may include a water-swellable tape 19 cand/or an armor between tube 18 and strength members 19 a; however, theuse of other suitable cable components are possible.

Additionally, a ribbon coupling force test may be used for modeling theforces applied to the optical waveguide(s) when subjecting a cable to,for example, pulling during installation of the cable. Although theresults between the ribbon pullout force and the ribbon coupling forcemay have forces in the same general range, the ribbon coupling force isgenerally a better indicator of actual cable performance.

Specifically, the ribbon coupling test simulates an underground cableinstallation in a duct by applying 600 pounds of tension on a 250 mlength of cable by placing pulling sheaves on the respective sheathes ofthe cable ends. Like the ribbon pullout test, this test is equallyapplicable to loose or bundled optical waveguides. However, othersuitable loads, lengths, and/or installation configurations can be usedfor characterizing waveguide coupling in other simulations. Then, theforce on the optical waveguide(s) along its length is measured from theend of cable. The force on the optical waveguide(s) is measured using aBrillouin Optical Time-Domain Reflectometer (BOTDR). Determining abest-fit slope of the curve normalizes the ribbon coupling force. Thus,according to the concepts of the present disclosure the coupling forceis preferably in the range of about 0.5 N/m to about 5.0 N/m, morepreferably, in the range of about 1 N/m to about 4 N/m. However, othersuitable ranges of coupling force may provide the desired performance.

Additionally, the concepts of the present disclosure can be employedwith other configurations of the dry insert. As depicted in FIG. 9, dryinsert 74 has a first layer 74 a and a second layer 74 b that includesdifferent suitable types of water-swellable substances. In oneembodiment, two different water-swellable substances are disposed in, oron, second layer 14 b so that tube assembly 10 is useful for multipleenvironments and/or has improved water-blocking performance. Forinstance, second layer 14 b can include a first water-swellablecomponent 76 effective for ionized liquids such as saltwater and asecond water-swellable component 78 effective for non-ionized liquids.By way of example, first water-swellable material is a polyacrylamideand second water-swellable material is a polyacrylate superabsorbent.Moreover, first and second water-swellable components 76,78 can occupypredetermined sections of the water-swellable tape. By alternating thewater-swellable materials, the tape is useful for standard applications,salt-water applications, or both. Other variations of differentwater-swellable substances include having a water-swellable substancewith different swell speeds, gel strengths and/or adhesion with thetape.

FIG. 10 depicts another embodiment of the dry insert. Dry insert 84 isformed from three layers. Layers 84 a and 84 c are water-swellablelayers that sandwich a layer 84 b that is compressible for providing acoupling force to the at least one optical waveguide. Likewise, otherembodiments of the dry insert can include other variations such at leasttwo compressible layers sandwiching a water-swellable layer. The twocompressible layers can have different spring constants for tailoringthe normal force applied to the at least optical waveguide.

FIG. 11 illustrates a dry insert 94 having layers 94 a and 94 baccording to another embodiment of the present disclosure. Layer 94 a isformed from a closed-cell foam having at least one perforation 95therethrough and layer 94 b includes at least one water-swellablesubstance; however, other suitable materials can be used for thecompressible layer. The closed-cell foam acts as a passivewater-blocking material that inhibits water from migrating therealongand perforation 95 allows an activated water-swellable substance oflayer 94 b to migrate radially inward towards the optical waveguide. Anysuitable size, shape, and/or pattern of perforation 95 that allows theactivated water-swellable substance to migrate radially inward toeffectively block water is permissible. The size, shape, and/or patternof perforations can be selected and arranged about the corner opticalwaveguides of the stack, thereby improving corner optical waveguideperformance. For example, perforations 95 can provide variation in dryinsert compressibility, thereby tailoring the normal force on theoptical waveguides for maintaining optical performance.

FIG. 12 depicts dry insert 104, which illustrates other concepts of thepresent disclosure. Dry insert 104 includes layers 104 a and 104 b.Layer 104 a is formed of a plurality of non-continuous compressibleelements that are disposed on layer 104 b, which is a continuouswater-swellable layer. In one embodiment, the elements of layer 104 aare disposed at regular intervals that generally correlate with the laylength of a ribbon stack. Additionally, the elements have a height hthat varies across their width w. Stated another way, the elements areshaped to conform to the shape of the optical waveguides they areintended to generally surround.

FIG. 13 depicts cable 130, which is another embodiment of the presentdisclosure that employs tube assembly 10. Cable 130 includes a sheathsystem 137 about tube assembly 10 for protecting tube assembly 10 from,for instance, crushing forces and environmental effects. In this case,sheath system 137 includes a water-swellable tape 132 that is secured bya binder thread (not visible), a pair of ripcords 135, an armor tape136, and a jacket 138. Armor tape 136 is preferably rolled formed;however, other suitable manufacturing methods may be used. The pair ofripcords 135 are generally disposed about one-hundred and eighty degreesapart with about ninety degree intervals from the armor overlap, therebyinhibiting the shearing of ripcord on an edge of the armor tape duringuse. In preferred embodiments, ripcords suitable for ripping through anarmor tape have a construction as disclosed in U.S. patent applicationSer. No. 10/652,046 filed on Aug. 29, 2003, the disclosure of which isincorporated herein by reference. Armor tape 136 can be either adielectric or a metallic material. If a dielectric armor tape is usedthe cable may also include a metallic wire for locating the cable inburied applications. In other words, the metallic wire makes the cabletonable. Jacket 138 generally surrounds armor tape 136 and providesenvironmental protection to cable 130. Of course, other suitable sheathsystems may be used about the tube assembly.

FIG. 14 depicts fiber optic cable 140. Cable 140 includes at least oneoptical waveguide 12 and a dry insert 14 forming a cable core 141 withina sheath system 142. In other words, cable 140 is a tubeless designsince access to the cable core 141 is accomplished by solely cuttingopen sheath system 142. Sheath system 142 also includes strength members142 a embedded therein and disposed at about 180 degrees apart, therebyimparting a preferential bend to the cable. Of course, other sheathsystems configurations such as different types, quantities, and/orplacement of strength members 142 a are possible. Cable 140 may alsoinclude one or more ripcords 145 disposed between cable core 141 andsheath 142 for ripping sheath 142, thereby allowing the craftsman easyaccess to cable core 141.

FIG. 15 depicts a fiber optic cable 150 having a plurality of tubeassemblies 10 stranded about a central member 151. Specifically, tubeassemblies 10 along with a plurality of filler rods 153 are S-Z strandedabout central member 151 and are secured with one or more binder threads(not visible), thereby forming a stranded cable core. The stranded cablecore has a water-swellable tape 156 thereabout, which is secured with abinder thread (not visible) before jacket 158 is extruded thereover.Optionally, aramid fibers, other suitable strength members and/or waterblocking components such as water-swellable yarns may be stranded aboutcentral member 151, thereby forming a portion of the stranded cablecore. Likewise, water-swellable components such as a yarn or tape may beplaced around central member 151 for inhibiting water migration alongthe middle of cable 150. Other variations of cable 150 can include anarmor tape, an inner jacket, and/or different numbers of tubeassemblies.

FIGS. 19 and 20 depict explanatory tubeless cable designs according tothe present disclosure. Specifically, cable 190 is a drop cable havingat least one optical waveguide 12 generally surrounded by dry insert 14within a cavity of jacket 198. Cable 190 also includes at least onestrength member 194. Other tubeless drop cable configurations are alsopossible such as round or oval configurations. FIG. 20 depicts atubeless figure-eight drop cable 200 having a messenger section 202 anda carrier section 204 connected by a common jacket 208. Messengersection 202 includes a strength member 203 and carrier section 204includes a cavity having at least one optical waveguide 12 that isgenerally surrounded by dry insert 14. Carrier section 204 can alsoinclude at least one anti-buckling member 205 therein for inhibitingshrinkage when carrier section 204 is separated from messenger section202. Although, FIGS. 19 and 20 depict the dry insert of FIG. 4a anysuitable dry insert may be used.

In other exemplary cable embodiments, a gel-free, or dry fiber opticribbon cable may include an inducement to couple the ribbon stack to thebuffer tube or jacket. An elongated tape may be employed inside thebuffer tube or jacket, surrounding the ribbon stack to facilitatecoupling and water blocking. By using, for example, such a tape wideenough to produce an overlapping portion around at least a portion ofthe ribbon stack, coupling may be induced due to the presence of atleast three layers of tape over a portion of the inner circumference ofthe buffer tube or jacket. Previously, tape was, for example, of such awidth relative to the tube size such that there was no overlap. Suchcoupling may be further enhanced by having a relatively large ratio oftube inner area to ribbon stack cross sectional area. Such enhancedcoupling may be achieved without increasing attenuation across theoptical fibers of the ribbon stack.

FIG. 21 depicts an exemplary embodiment of a fiber optic ribbon cable300 having a jacket 310, a buffer tube 320 disposed in jacket 310, afiber optic ribbon stack 330 and an elongated tape 340 disposed aboutribbon stack 330. Ribbon stack 330 extends longitudinally within buffertube 320. In some embodiments, buffer tube 320 may not be present,leaving jacket 310 to function as both jacket and buffer tube. Elongatedtape 340 may include two opposing edges, 342, 344. Elongated tape 330may, in exemplary embodiments, extend along ribbon stack 330, wrappingaround ribbon stack 330, for example, with at least a portion of oneopposing edge 344 tucking between the other opposing edge 342 and ribbonstack 330, defining an overlapping portion 350. Ribbon stack 330 may bemade from optical fiber ribbons 331, and may be oriented in a helicaltwist. Ribbon stack 330 may include up to 144 optical fibers, an inexemplary embodiments may have 72 optical fibers.

As shown in FIG. 22, ribbon stack 330 has an average cross sectionalribbon area 336 defined by average stack height 332 and average stackwidth 334. In exemplary embodiments buffer tube 310 has an average crosssectional inner area 326 bounded by average inner perimeter 324, anddefined by, for example, average inner width 322. Buffer tube 310 may insome embodiments define a generally circular profile, making the areacalculation an application of the formula for the area of a circle, asknown, having a diameter with the value of average inner width 322. Inexemplary embodiments inner area 326 and ribbon area 336 define a ratioof about 0.30 or greater. In other words, ribbon area 336 may representabout 30% or more of inner area 326.

Elongated tape 340 may reside in the balance of inner area 326, as shownin FIG. 23, substantially surrounding ribbon stack 330. As stated above,elongated tape 340 may have two opposing edges 342, 344 that traversethe length of elongated tape 340. In exemplary embodiments overlappingportion 350 may be defined, for example by one edge, for example, edge342, tucking beneath the other edge, for example, edge 344, sandwichingan outside layer 343 and a tucked in layer 345 of elongated tape 340between buffer tube 320 and ribbon stack 330. Overlapping portion 350may partially surround ribbon stack 330 as depicted by an angularoverlap measurement 352, for example, of at least 45 degrees. Inexemplary embodiments, overlap measurement 352 of overlapping portion350 may be from about 90 degrees to about 180 degrees, and in yet otherexemplary embodiments may be about 130 degrees.

An imaginary diametric line 362 traversing cable 300 and crossingoverlapping portion 350 may encounter, for example, three layers 364,366, 368 of elongated tape 340. Such overlapping may insure an adequatelinear distance 354, shown in FIG. 24, of overlapping portion to providea large range of three layer tape region 360, enhancing ribbon stackcoupling. Linear distance 354 may be from about four millimeters toabout six millimeters. As defined herein, an “overlap” need not becontinuous or uniform along the entire length of ribbon cable 300. Inexemplary embodiments, overlapping portion 350 may extend longitudinallyalong ribbon stack 330 for a distance of at least one meter.

Shown in FIG. 25, elongated tape 340 may, in exemplary embodiments, bemade from a nonwoven polyester material and include water blockingmaterial, for example, superabsorbent polymer, though other materialsmay be contemplated. Elongated tape 340 may have a width 346 greaterthan 14 millimeters, and other embodiments may have a width in the rangeof about 18 millimeters to about 25 millimeters. In yet other exemplaryembodiments elongated tape 340 may be from about 20 millimeters to about22 millimeters, e.g., 21 millimeters. In exemplary embodiments,elongated tape 340 of ribbon cable 300 may not require the applicationof adhesives or glues.

The presence of three layers 364, 366, 368 of elongated tape 340,enabled by overlapping portion 350, provides coupling of ribbon stack330 relative to jacket 310 or buffer tube 320. Any attempted movement ofribbon stack 330 may be met by resistance from elongated tape 340,effectively binding ribbon stack 330 to the interior of jacket 310 orbuffer tube 320. In addition to overlapping portion 350, elongated tape340 may include other longitudinal features disposed along the length ofthe cable, for example, folds, wrinkles, creases, corrugations, quiltingand combinations of the same, which may further enhance the couplingforce of ribbon stack 330. In some embodiments, ribbon stack 330 mayhaving a coupling force relative to jacket 310 or buffer tube 320 ofgreater than or equal to 0.39 Newtons per meter (N/m) for a 30 meterlength of ribbon cable 300. This provides for 0.1625 Newtons per fiberper 30 meters of cable length. In other embodiments, the coupling forcemay be from about 1.67 N/m to about 2.66 N/m for a 30 meter length ofribbon cable 300. In yet other embodiments, the coupling force may befrom about 2.0 N/m to about 2.33 N/m for a 30 meter length of ribboncable 300. In exemplary embodiments, the coupling force may be about2.25 N/m for a 30 meter length of ribbon cable 300. In other words,ribbon stack 330, having, for example, 72 fibers, may have a couplingforce of about 68 Newtons. As shown in FIG. 26, a 72 fiber cable nothaving overlapping portion 350 has a coupling force of about 7 Newtons,which may be stated to be 0.0972 Newtons per fiber over a 30 meterlength of cable, or only about 60% of a minimum provided by overlappingportion 350.

In exemplary embodiments, ribbon cable 300 may further include an armorlayer disposed between buffer tube 320 and the jacket 310. The armorlayer (not shown) may be a dielectric armor layer or a metallic armorlayer.

A method of manufacturing ribbon cable 300 may be referenced above, andin FIG. 6. In addition to the procedures above, the method may alsoinclude the step of paying off a plurality of optical fiber ribbons,forming ribbon stack 330. In exemplary embodiments, the method mayinclude paying off at least one elongated tape 340, placing elongatedtape 340 around the plurality of optical fiber ribbons so that theelongated tape overlaps on itself, forming overlapping portion 350, theoverlapping portion at least partially surrounding the plurality ofoptical fiber ribbons, forming a core. Buffer tube 320, for example, maybe extruded around the core. Jacket 310 may be extruded around buffertube 320.

Coupling force may be induced in fiber optic ribbon cable 300. Forexample, when buffer tube 320 is around the core, buffer tube 320 maybe, for example, a polymer extruded in a molten state. By cooling buffertube 320, buffer tube 320 may contract around the core, inducing thecoupling force between the ribbon stack, the elongated tape, theoverlapping portion and the buffer tube of about 0.39 N/m or greater fora 30 meter length of cable.

Advantages of above-described embodiments include the ability to changeor “tune” the coupling force by adjusting the amount of the overlap ofthe tape or by changing the twist lay of the stack of ribbons. Forexample, as shown in FIGS. 21, 23, and 24, in at least some of theabove-described embodiments, the corners of a rectangular stack ofribbons form the outermost projections of the ribbon stack and therebycontact the tape and provide some or all of the coupling force viainteraction with the tape (e.g., compression of the tape(s) by thecorners of the stack). With the stack twisted, the corners of the stackonly contact the overlapping tape section within the tube atintermittent locations along the length of the cable, thereby providingintermittent coupling points or portions; where, between the points orportions of intermittent coupling, the stack of ribbons may be lesscoupled or not directly coupled at all to the tube, allowing greaterfreedom of ribbon movement when compared to the intermittent couplingpoints or portions. As such, increasing the twist rate (i.e., decreasingthe lay length of the stack) increases the number of intermittentcoupling points or portions between the stack and the overlappingportion of the tape, thereby increasing the overall coupling andpull-out force. Alternatively, or in addition thereto, increasing theamount of overlap of tape (e.g., 130-degrees of the interior of thetube, as opposed to just 45-degrees of overlap) accordingly increasesthe length that the corners of the ribbon stack, twisting within thetube relative to the overlap, contact or interface with the overlap ateach respective intermittent coupling point or portion, therebycorrespondingly increasing the coupling force. Coupling may be increasedby changing other parameters as well, such as by decreasing the tubediameter (influencing the ratio of stack-to-inner-tube-area), increasingthe ribbon stack size (influencing the ratio ofstack-to-inner-tube-area), increasing the tape thickness, and byadjusting or changing other parameters; and the opposite may be true aswell, that coupling force between the ribbon stack and the tube by wayof the tape may be reduced by reversing such parameters. With that said,increasing the amount of tape overlap and/or increasing the rate oftwist in the ribbon stack (i.e., decreasing the lay length) are tworelatively simple ways to “tune” the coupling force, so as to achievethe desired coupling and/or a coupling force within the ranges disclosedabove (or other coupling forces).

Many modifications and other embodiments of the present disclosure,within the scope of the appended claims, will become apparent to askilled artisan. For example, optical waveguides can be formed in avariety of ribbon stacks or configurations such as a stepped profile ofthe ribbon stack. Cables according to the present disclosure can alsoinclude more than one optical tube assembly stranded helically, ratherthan S-Z stranded configurations. Additionally, dry inserts of thepresent disclosure can be laminated together as shown or applied asindividual components. Therefore, it is to be understood that thedisclosure is not limited to the specific embodiments disclosed hereinand that modifications and other embodiments may be made within thescope of the appended claims. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation. The disclosure has been described withreference to silica-based optical waveguides, but the inventive conceptsof the present disclosure are applicable to other suitable opticalwaveguides and/or cable configurations.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred. It will be apparent to those skilledin the art that various modifications and variations can be made withoutdeparting from the spirit or scope of the disclosure. Sincemodifications combinations, sub-combinations and variations of thedisclosed embodiments incorporating the spirit and substance of thedisclosure may occur to persons skilled in the art, the disclosureshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A fiber optic ribbon assembly, comprising: atube; a plurality of fiber optical waveguides extending longitudinallywithin the tube; and a dry insert surrounding the plurality of fiberoptic ribbons, wherein the dry insert comprises a compressible layersandwiched between two water-swellable layers.
 2. The assembly of claim1, wherein the tube is a jacket.
 3. The assembly of claim 1, furthercomprising at least one strength member surrounded by the jacket.
 4. Theassembly of claim 1, wherein the plurality of optical waveguidesincludes at least one single-mode optical fiber.
 5. The assembly ofclaim 4, wherein the plurlity of optical waveguides form a ribbon stack.